I did a little NGram on it. Obviously, the limitations of Ngram is that it only captures usage in written documents available to Google. As a result, Ngram will tend to have more recent spikes for some terms simply as a function of the availability of scanned, searchable text, etc. However, it is still a pretty good indication of a term's use.
The term bunker buster was indeed around since the 1940s meaning more or less what it means today, though there were other uses. But its use is extremely rare until the 1980s when the defense industry decides to use it as a selling tool for appropriations committees. Hence, the spike in the 80s is mostly associated with Congressional documents. There is additional use in media for the first Gulf War. Notably, the term is mostly non-existent during the entirety of the Vietnam period (for which we have plenty of text-searchable documents), which at least suggest it was not in widespread use even in military contexts after World War II.
The term really takes off (see the NGram link) in the early 2000s with the war on terror, a massive media-driven spike in usage. It is, in short, a marketing gimmick for the military industrial complex at best, and a little magical fairy tale invented by the US media at worst. Like I said, phony baloney.
https://books.google.com/ngrams/graph?content=bunker+buster&year_start=1800&year_end=2022&corpus=en&smoothing=3
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